This is far too easy. The tree to the right of the screen is full of fruit. When you eat a piece it will grow back (around five times per piece.) It also has a heart fruit (invincibility) which will grow back twice. To start, Bowser will fly about on green ghosts. The easiest way to hit him is to get rid of all of your shells and grab a bomb with your tongue. Throw this and try to hit him with it. After hitting him three times the ghosts will disappear. (If you are injured at all, eat some fruit.) Now he'll jump around the screen. Once again throw bombs, remember that they rebound off walls unlike shells allowing backhits. Another three hits and you've won. Incidently if you have the black and white Yoshi's they'll be in the ending too.